Service providers of wireless communication systems are continuously working on improving the wireless coverage of their respective systems. They employ such techniques as providing more base transceiver stations (BTS) within a given area, providing BTS in areas not previously covered, and improving the performances of BTS and network equipment to reduce the probability of dropped calls and signal interference due to poor radio frequency (RF) environments.
Among these on-going developments is the improvement of wireless coverage inside buildings, dwellings, and other structures. Buildings generally have an adverse effect on the RF environment of a wireless communication system. They are constructed out of many RF affecting materials, such as grounded steel frames, that interfere with and/or reduce the signal strength of wireless communication signals inside of the building.
Attempts have been made at improving the wireless coverage inside buildings. One of these is to employ a repeater outside of a building and distributed antenna modules strategically placed inside of the building. In a BTS, the digital service signal (DSS) modulates an RF carrier, generating an analog RF signal (i.e., the RF service signal (RSS)), which is then sent through an antenna feed from the BTS to an antenna for propagation over the air. For a distributed antenna system (DAS), the RSS is sent over a physical medium to remote antennas, instead of being radiated over the air at the BTS.
For in-building coverage, in the forward link, the RSS is sent to distributed antenna modules via a dedicated physical medium, such as an optical fiber or coaxial cable, distributed within a building. The distributed antenna modules then transmits the RSS wirelessly to SUs (e.g., wireless communication devices, such as handsets) within the building. Similarly, in the reverse link, a distributed antenna module receives the RSS from one or more subscriber units, and sends it via the broadband physical medium for transmission back to the BTS.
There are several drawbacks with such a system. First, the transmission of the RSS within the building, as discussed above, typically requires a dedicated physical medium, such as optical fibers or coaxial cables. In current implementations, the RSS is sent over the physical medium as the analog RF signal received from the antenna feed. Alternatively, the RSS may be sampled, at a rate at least twice that of the bandwidth, according to the Nyquist theorem, to create a digitized representation of the analog RF signal, and then the RSS is sent to the DAS.
These methods require much greater bandwidth than the original DSS generated inside of a BTS. Since dedicated optical fibers or coaxial cables are required to provide enough bandwidth for the DAS, the medium is typically relatively expensive. Second, the labor associated with “wiring” the dedicated physical medium inside of a building is also typically relatively expensive. Third, if the analog RSS is sent across the physical medium, it is more susceptible to signal degradation due to noise, and/or inter-modulation products if two or more signals are transmitted.